Bianchigirl: I'll get a pic and serial number when I'm next home. I had never heard of a 105 Sport SX either. It came with indexed 6-speed 105, with beefy single pivot calipers (silvery grey, not the blueish anodized ones) which might date it a bit better -- I think that rules out '85. I don't think anything has been changed out because it came with 105 pedals, headset, hubs, and so on. Could this be some Canadian oddity?

A friend now has the frame from my slightly-too-small '87, which had Suntour Alpha 5000 (beautiful stuff). (I bought two mothballed Sport SXs within a few months of each other, from Kijiji.)

Joejack: I live in Winnipeg, which has no natural hills and less than 100' elevation change within the city. Interloc's $50 (+ shipping to Canada) freewheels don't do much better than my 6sp 13-24 (13-15-17-19-21-24). I do long, spirited group rides in the flat plain around here, and would like closer ratios at the high end. A 12t would be nice for tailwindy days as well. If someone made a 13-19 7sp freewheel I'd be all over it, but my only option there is ludicrously expensive non-Hyperglide Regina or Sachs from eBay. The reason I'm considering re-using parts of the wheel with a new 105 hub is so my rims will match -- I can't find any modern rims that looks similar.